The variation of Nγ with footing roughness using the method of characteristics

By using the method of characteristics, the effect of footing–soil interface friction angle (δ) on the bearing capacity factor N_γ was computed for a strip footing. The analysis was performed by employing a curved trapped wedge under the footing base; this wedge joins the footing base at a distance B_t from the footing edge. For a given footing width (B), the value of B_t increases continuously with a decrease in δ. For δ=0, no trapped wedge exists below the footing base, that is, B_t/B=0.5. On the contrary, with δ=?, the point of emergence of the trapped wedge approaches toward the footing edge with an increase in ?. The magnitude of N_γ increases substantially with an increase in δ/?. The maximum depth of the plastic zone becomes higher for greater values of δ/?. The results from the present analysis were found to compare well with those reported in the literature. Copyright © 2008 John Wiley & Sons, Ltd.     

Seismic response of bridge pier on rigid caisson foundation in soil stratum

An analytical method to study the seismic response of a bridge pier supported on a rigid caisson foundation embedded in a deep soil stratum underlain by a homogeneous half space is developed. The method reproduces the kinematic and inertial responses, using translational and rotational distributed Winkler springs and dashpots to simulate the soil-caisson interaction. Closed-form solutions are given in the frequency domain for vertical harmonic S-wave excitation. Comparison with results from finite element （FE） analysis and other available solutions demonstrates the reliability of the model. Results from parametric studies are given for the kinematic and inertial responses. The modification of the fundamental period and damping ratio of the bridge due to soil-structure interaction is graphically illustrated.     

水平荷载下套管桩基的非线性响应分析

提出了用新型套管桩基来提高海洋平台桩基水平承载力和减小平台响应幅值。采用p-y曲线法来模拟桩土间的相互作用,对套管桩基进行非线性响应分析,研究了套管的埋深和宽度对桩身变形和土抗力的影响,并与普通桩基进行了对比分析。研究表明,套管桩基能充分发挥桩土间的相互作用,提高桩基的水平承载力,减小桩基的水平响应。     

海洋桩基工程中的钙质土

本文在简述钙质土成因和组成的基础上，介绍分析了这种土的物理力学性质，尤其是其受力后变化的特性；说明了钙质土与桩的相互作用特性；对钙质土中导管架平台桩基设计的土工调查及其有关设计参数的选用作了论述     

Impedances of rigid cylindrical foundations embedded in transversely isotropic soils

A complete formulation and implementation for assessment of the response to dynamic loads of cylindrical rigid structures embedded in transversely isotropic elastic half‐spaces is presented. The analysis is performed in the frequency domain and the steady‐state structure response is obtained. The method is based on a non‐singular version of the indirect boundary element method which uses influence functions, instead of Green's functions, as fundamental solutions. These influence functions are the response of an elastic half‐space to distributed, internally applied loads. The proposed method imposes full bonding contact between the foundation and the surrounding soil. Numerical results for displacement (vertical and horizontal) and rotation (twisting and rocking) impedances, showing the influence of the soil anisotropy, are presented. Results for the soil–structure interface tractions and for the displacement field throughout the half‐space are also shown. Copyright © 2006 John Wiley & Sons, Ltd.     

Failure envelopes and plastic potentials for eccentrically loaded surface footings on undrained soil

The failure envelope in V–M space for surface foundations on undrained material under eccentric loading can be determined using an extended version of the scaling (or effective area) concept of Meyerhof. A similar displacement transformation allows production of the plastic potential. The two‐dimensional finite element analyses of fully attached foundations subject to combined vertical (V) and moment (M) loading have been used to calculate appropriate scaling points for deduction of the failure envelope and plastic potential. Failure envelopes and plastic potentials are presented for footings on uniform and non‐uniform undrained material and it is seen that the equivalent ‘critical state’ or ‘parallel point’ lies slightly beneath the peak moment capacity. For accurate prediction of failure envelopes for footings on non‐uniform strength soil, consideration must be made of the apparent reduction of the soil heterogeneity as the area of footing in contact with the soil decreases. Copyright © 2001 John Wiley & Sons, Ltd.     

Multicriterial analysis in the investigation of favorable areas for edifications with shallow and deep foundations in the Municipality of Campos dos Goytacazes — Rio de Janeiro, Brazil

The Municipality of Campos dos Goytacazes is located on the northern coast of Rio de Janeiro, Brazil. The city developed on a floodplain and as a consequence of this occupation it has experienced problems with the water table level, drainage system, soil carrying capacity and aquifers' contamination. The purpose of this paper was to accomplish a geological and environmental study, producing interpretive and derived geotechnical maps to analyze the degree of aptitudes or restrictions of the physical environment for urban expansion. In order to do this, the methodology of multicriterial analysis was used, combined with pedological indicators resulting in the elaboration of the Favorability Maps for Buildings (Shallow and Deep Foundations). The remote sensing tools, GIS and GPS, sped up the elaboration of the Information Plans. The maps generated in this work allow us to indicate problems in the physical environment serving as a guide to urbanization. It was verified that the city expands into unsuitable areas and it is recommended as areas for expansion those considered favorable in the outcomes of this research.     

Progressive failure analysis of shallow foundations on soils with strain-softening behaviour

This paper presents a finite element approach to analyse the response of shallow foundations on soils with strain-softening behaviour. In these soils, a progressive failure can occur owing to a reduction of strength with increasing the plastic strains induced by loading. The present approach allows this failure process to be properly simulated by using a non-local elasto-viscoplastic constitutive model in conjunction with a Mohr–Coulomb yield function in which the shear strength parameters are reduced with the accumulated deviatoric plastic strain. Another significant advantage of the method is that it requires few material parameters as input data, with most of these parameters that can be readily obtained from conventional geotechnical tests. To assess the reliability of the proposed approach, some comparisons with experimental results from physical model tests are shown. A fairly good agreement is found between simulated and observed results. Finally, the progressive failure process that occurs in a dense sand layer owing to loading is analysed in details, and the main aspects concerning the associated failure mechanism are highlighted.     

含扩径桩的群桩基础竖向承载性状数值分析

为探讨扩径缺陷桩对竖向荷载作用下群桩基础工作性状的影响,建立了一个群桩基础数值分析模型。采用三维非线性有限元/无限元方法对正常桩基础及含有浅部或深部扩径缺陷桩的群桩基础进行了一系列对比分析。分析结果初步揭示了竖向荷载作用下含扩径缺陷桩的桩基础基本工作特性,得出了扩径缺陷对群桩各桩间轴力分布及承台弯矩分布影响的基本规律性。研究成果不仅有助于认识和合理判断扩径桩的工作机制,而且对评价有扩径缺陷的桩基承载性状、选择缺陷处理技术及桩与承台的结构设计都具有重要的实际意义     

Dynamic stiffness of monopiles supporting offshore wind turbine generators

Very large diameter steel tubular piles (up to 10 m in diameter, termed as XL or XXL monopiles) and caissons are currently used as foundations to support offshore Wind Turbine Generators (WTG) despite limited guidance in codes of practice. The current codes of practice such as API/DnV suggest methods to analysis long flexible piles which are being used (often without any modification) to analyse large diameter monopiles giving unsatisfactory results. As a result, there is an interest in the analysis of deep foundation for a wide range of length to diameter (L/D) ratio embedded in different types of soil.This paper carries out a theoretical study utilising Hamiltonian principle to analyse deep foundations ($L/D\ge 2$) embedded in three types of ground profiles (homogeneous, inhomogeneous and layered continua) that are of interest to offshore wind turbine industry. Impedance functions (static and dynamic) have been proposed for piles exhibiting rigid and flexible behaviour in all the 3 ground profiles. Through the analysis, it is concluded that the conventional Winkler-based approach (such as p–y curves or Bean-on-Dynamic Winkler Foundations) may not be applicable for piles or caissons having aspect ratio less than about 10 to 15. The results also show that, for the same dimensionless frequency, damping ratio of large diameter rigid piles is higher than long flexible piles and is approximately 1.2–1.5 times the material damping. It is also shown that Winkler-based approach developed for flexible piles will under predict stiffness of rigid piles, thereby also under predicting natural frequency of the WTG system. Four wind turbine foundations from four different European wind farms have been considered to gain further useful insights.